By manipulating the environment of the excised, perfused, bullfrog retina while monitoring the electrical activity of the photoreceptors, an attempt will be made to better define the fundamental processes which are related to the photoreceptor's response to a light stimulus. Specific experiments will be performed with respect to the influence of calcium ions, temperature, and ethyl alcohol on the function of the photoreceptors. The sensitivity of the photoreceptors, the amplitude of the late receptor potential, the time course of rapid dark adaptation and the adaptation pattern known as the suppression-recovery effect will all be studied. By employing an appropriate background illumination and/or by utilizing a multi-flash stimulus presentation rod and cone activity will be observed independently in the same retina in the course of a single experiment. In order to isolate the responses of the photoreceptors from the influence of the more proximal retinal cells, all solutions employed throughout the course of the study will contain sodium aspartate.